The invention relates as indicated to a method and apparatus for producing even heating of products by microwaves, and is particularly useful in the heating of food products.
Apparatus for pasteurizing by means of microwaves is known from German Patent No. 3,432,341. There is disclosed therein an oblong microwave treatment chamber with a continuous conveyor belt passing through the chamber. Microwave input channels are led into the treatment chamber and temperature probes are arranged. By means of this apparatus, a step-by-step reduction of the microwave energy to be input is carried out in each case in three successive chambers. If the product to be treated, for example a ready meal, is to be subjected to a pasteurizing operation, the achievement of an even temperature for all of the various components contained in the package is of great importance. It is very difficult to meet this demand, because the individual products, for example different pharmaceutical or food products, have a different heat requirement for reaching an even temperature.
In prior art methods, the temperature of the product was taken as a criterion which the treatment temperature, for example the pasteurization temperature, had first reached. The upper treatment temperature was the maximum, critical temperature which it was not permitted to exceed, in order to avoid temperature-caused damage. The remaining products contained in the package, for example gravy, consequently did not reach the pasteurization temperature at all, because a further increase of the overall temperature which would have been necessary for pasteurizing the gravy would have necessarily led to damage to the other products.